1. Field of the Invention
The object of the invention is to provide a solder bath which is also suitable for the dip-tinning of elongated components. In particular, the solder bath should be of such a nature that within the workpiece dipping or transit zone the molten solder is uniformly pervaded by ultrasonic waves. Cancellation phenomena as a consequence of interference stemming from different sonotrodes or the walls of the vessel, are avoided.
2. Prior Art
In the German Auslegeschrift No. 2,107,862 a solder bath having a vessel comprising a sonotrode extending from the base of the vessel and affixed thereto by means of a collar and a set of sealing sleeves wherein the sonotrode is located in the neighborhood of the plane of a node of oscillation. By means of this design of the sonotrode seals at the point of penetration of the base, the ultrasonic oscillations produced by the sonotrode are insulated from the base of the vessel so that interference phenomena and damping in the molten solder are prevented. Solder baths of this kind are used, for example, for the fluxless soldering of small components which are dipped into a solder bath through which the ultrasonic waves are transmitted. This method of soldering makes it possible to produce a firmly adhering tinned coating on the components which are to be soldered without the need for a flux and without the associated disadvantages such as subsequent rinsing away of flux residues and damage to components due to flux vapor. In a solder bath of this kind, however, it is not possible to satisfactorily solder long narrow components such as pin strips and plug strips in the manner hereinbefore described because the wide sonotrodes which this necessitates result in a non-uniform amplitude distribution over their end faces and therefore also within the solder located above or flowing over the end faces of the sonotrodes. A non-uniform amplitude distribution precludes the development of a locally required cavitation effect at the locale of the component being soldered, resulting in the occurence of faults in the solder application to the component.
U.S. Pat. No. 3,266,136 depicts a solder bath in which several sonotrodes are extended through the base of a solder channel. Each sonotrode is surrounded by a seal at a point at which it penetrates through the base. In one embodiment, the sonotrodes are coupled with a common oscillator plate from which the acoustic waves are radiated into the molten solder. A plate of this kind, however, has its own oscillatory characteristics wherein, even assuming that the sonotrodes oscillate co-phasally, a non-uniform amplitude distribution develops in the solder melt. An arrangement of this kind, because of the seal which each sonotrode requires and the other fixing elements, necessitates a larger interval between the individual sonotrodes; even if the common oscillator plate is dispensed with. This results in the development of acoustic difficiency zones in the solder melt within the spaces between the sonotrodes.
The German Offenlegungsschrift No. 1,597,015 depicts a device for radiating ultrasonic oscillations in liquid media. The device comprises a bath vessel having several sonotrodes extending through the base of the vessel, each equipped with an ultrasonic head. The ultrasonic heads are connected in parallel in the excitation circuit so as to oscillate co-phasally. However, here again the sonotrodes are spaced far apart. Because of this and of the nature of the method by which the sonotrodes are taken through the base of the vessel, the co-phasality of the ultrasonic oscillations within the bath liquid, engendered by the parallel arrangement, is disturbed by heterodyning effects.